“Brake-by-wire” brake systems are becoming increasingly widespread in automotive engineering. In addition to a main brake cylinder, which is actuatable by the vehicle driver, hydraulic “brake-by-wire” brake systems often includes an electrically controllable pressure supply device, by which, in the “brake-by-wire” operating mode, the wheel brakes are actuated either directly or via the main brake cylinder. In order to impart a pleasant and expected pedal sensation to the vehicle driver in the “brake-by-wire” operating mode, the brake systems usually includes a brake pedal sensation simulation device, which is operatively connected, for example, to the main brake cylinder. A setpoint value generator is provided to control the brake system, which setpoint value generator, for example, evaluates the electrical signals of one or more sensors for sensing the driver's braking command (actuation command) in order to determine a setpoint value for controlling the pressure supply device. In these brake systems, the pressure supply device can also be actuated, however, on the basis of electronic signals without active input from the driver. These electronic signals can be output, for example, by an electronic stability program (ESC) or distance control system (ACC), and so the setpoint value generator determines a setpoint value for controlling the pressure supply device on the basis of these signals.
A method for controlling an electrohydraulic brake system for motor vehicles having an electronically controllable pressure supply device which is connected to hydraulically actuatable wheel brakes, is described in WO 2011/154275 A1. The pressure supply device includes a cylinder-piston assembly having a hydraulic pressure chamber, the piston of which can be displaced relative to a rest position by an electromechanical actuator. For the purpose of control, a pre-pressure actual value and a pre-pressure setpoint value are determined, which are fed, as input variables, to a control device. The cylinder-piston assembly is controlled by the control device in such a way that the pre-pressure setpoint value in the hydraulic pressure chamber is set via displacement of the piston.
In addition, “brake-by-wire” brake systems having at least one electromechanically actuatable wheel brake are known. For example, EP 1 611 365 B1 discloses an actuating unit for an electromechanically actuatable disk brake for motor vehicles, which is disposed on a brake caliper, in which two friction linings, each of which interacts with a lateral surface of a brake disk, are disposed so as to have limited displaceability, wherein one of the friction linings can be brought into engagement with the brake disk directly by the actuating unit by means of an actuating element and the other friction lining can be brought into engagement with the brake disk by means of the effect of a reaction force applied by the brake caliper, wherein the actuating unit consists of an electric motor, a first reduction gear operatively disposed between the electric motor and the actuating element, and a second reduction gear disposed between the electric motor and a part of the first reduction gear, and wherein assigned to the actuating unit is an electronic control unit, which is used to control the electric motor.
A method for controlling a brake system having a hydraulic cylinder-piston assembly, as the pressure supply device, which can be driven by an electromechanical actuator is described in DE 10 2012 200 494 A1. In this case, a manipulated variable for the electromechanical actuator is determined as a function of a measured pressure actual value and a specified pressure setpoint value. If certain conditions are present, instead of the measured pressure actual value, a calculated model pressure actual value is determined and the manipulated variable for the electromechanical actuator is determined on the basis of the model pressure actual value and the specified pressure setpoint value. In this case, the model pressure actual value is calculated according to a specified linear function from the present position of the pressure supply device. The specified linear function is therefore used to calculate an alternative pressure actual value for the control, instead of the measured pressure actual value. The method is used exclusively for quickly bridging, in particular great, clearance of the wheel brake(s) connected to the pressure supply device. A general improvement of the accuracy of the closed-loop response is therefore not achieved.
A problem addressed by the present invention is that of providing a method for controlling an electromechanical actuator, and a control device for an electromechanical actuator, which enables a more precise setting of specified setpoint values of a controlled variable or (time) setpoint value curves.
This problem is solved according to the invention by a method and by a control device described herein.